Microsoft shuts down spam behemoth Rustock, reduces worldwide spam by 39% - Microsoft's Digital Crimes Unit, working with federal law enforcement agents, has brought down the world's largest spam network, Rustock. Rustock, at its peak, was a botnet of around 2 million spam-sending zombies capable of sending out 30 billion spam email per day. Microsoft's wholesale slaughter of Rustock could reduce worldwide spam output by up to 39%.From cw